e2e: preload httpbin and grpcbin images

[roobre]

Description

This PR adds the kennethreitz/httpbin and moul/grpcbin to the e2e cluster before tests are run. By doing this, images will be ready when e2e scenarios run, so the time that they take to download won't count against the test timeout, reducing test flakyness.

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make test) and all tests pass.
• I have run relevant integration test locally (make integration-xxx for affected packages)
• I have run relevant e2e test locally (make e2e-xxx for disruptors, or cluster related changes)
• Any dependent changes have been merged and published in downstream modules
  

[pablochacin]

I would prefer to load these images in the corresponding test setup, instead of by default, as I expect the images needed for each test to change over time.

[roobre]

@pablochacin That makes sense. For this to work though, I had to expose a method to load images after the cluster has been created. Otherwise, these images wouldn't get preloaded when running make e2e-xxx as (as far as I understand it) cluster creation options are ignored if E2E_REUSE is true and a cluster with the same name already exists.

LMK what you think about this approach.

[pablochacin]

I find this code hard to read, I think we could offer a helper function for extracting the images, but this can be in a follow-up PR.

[roobre]

Agreed, it is a bit confusing. I also considered storing those images on an exported constant, and have both fixtures and this code use those constants, but seemed easier to forget than this.

[pablochacin]

Awesome! I like this approach of dynamic image loading